Method of manufacturing a heat exchanger for cooling and heating purposes

ABSTRACT

A method and apparatus for manufacturing heat exchangers for cooling and heating purposes from substantially rectangular tube elements alternating with surface-enlarging members in the form of thin pleated metal strips being advanced, pressed against each other, through a heating zone for soldering together and thereafter discharged through a cooling zone for cooling the solder to fusion temperature, the advancing movement being opposed by a constant retarding force means acting in a direction counter to the direction of advance.

The present invention relates to a method in manufacturing heatexchangers for cooling and heating purposes, said heat exchangerscomprising a predetermined number of tubes with substantiallyrectangular cross section alternating with intermediatesurface-enlarging members in the form of pleated, thin metal strips,united at their peaks by means of solder to the wider sides of the tubesand maintaining a uniform pitch between the tubes, starting from tubeelement pieces and surface-enlarging members of predetermined lengths.

The invention also relates to an apparatus for carrying out the methodof manufacturing heat exchangers for cooling and heating purposes inaccordance with the invention.

In the manufacture of heat exchangers for car radiators, for example, itis known in the art to manually alternately arrange tubes with a flatconfiguration and surface enlarging members in the form of pleated, thinmetal strips in frames or the like, where either the tubes or thesurface-enlarging members have been provided with solder. Subsequent toall the details required in such a heat exchanger being inserted in theframe, the stack of details situated therein is compressed with the aidof a bridging member or the like so that suitable abutment is obtainedbetween the details incorporated.

After these steps have been taken, the stack of details enclosed in thisway is subjected to heating so that the solder melts, whereafter thestack is cooled so that the peaks of the thin metal strips are solderedto the tubes and an intimate heat-conducting metallic union isestablished.

With the intention of obtaining optimum utilization of the material inmanufacturing heat exchangers of the kind in question here, with respectto heat conducting ability and with regard to the desire of reducing theweight of the heat exchanger to the lowest value, it has been previouslyproposed, inter alia, to use copper strips for the production of thesurface enlarging members, said strips having been rolled down to verysmall thicknesses.

However, in the manual handling of such surface-enlarging members builtup from ever thinner copper strip, it has been found that these thinmeans are extremely easily deformed, which in turn has the consequencethat there occur incomplete solder joints between the surface-enlargingmembers and the tube elements.

To remove this drawback, the surface-enlarging members have beenproduced in the form of pleated copper strips, soldered together with anintermediate flat metal strip to give the means greater stiffness andless fragility in handling.

These steps have not been found sufficient to master the said problemeither, at least with regard to the manual handling.

On the basis of this experience it has been sought to eliminate manualhandling and automate production of the heat exchangers in question, toavoid the risks of damage caused manually. The object of the inventionis consequently to provide a method as above, which is substantiallycharacterized in that the tube element pieces and surface-enlargingmembers are continuously placed in abutment with each other, and in thisposition are forcibly fed in their transverse direction while overcominga predetermined restraining force, first through a heating zone formelting the solder to soldering temperature and thereafter through acooling zone for cooling the melted solder to fusion temperature so thatthe peaks on the pleated metal strip are brought into intimate solderedunion with adjacent tube member pieces.

The apparatus in accordance with the invention for carrying out themethod of manufacturing heat exchangers for cooling and heating purposesis mainly characterized in that the apparatus has an advancing trackprovided with a charging and a discharging end for continuous forcedadvance in its transverse direction of the tube element pieces andsurface-enlarging members alternately abutting in intimate mutualcontact, a force feeder being coordinated with the feed track forcarrying out said forced advance of the tube element pieces andsurface-enlarging members, from said charging end towards saiddischarging of the feed track, in that there is a retarding orrestraining means for continuously counteracting the forced advancemovement on the discharge side with a constant predeterminedcounteracting force, and in that the feed track, starting from thecharging end, first extends through a heating zone for melting thesolder to soldering temperature, then through a cooling zone for coolingthe melted solder to a fusion temperature, the peaks of the pleatedmetal strip thus being brought into intimate heat conducting metallicunion with the adjacent tube element pieces.

The invention will now be described in detail while referring to anembodiment example thereof schematically shown on the accompanyingdrawing, and in conjunction therewith further characterizing features ofthe invention will be disclosed.

On the drawing, FIG. 1 is an end view of loosely assembled tube elementsand surface-enlarging members in the form of pleated thin metal strip,the latter consisting in the shown embodiment of two pleated metalstrips and an intermediate flat metal strip, FIG. 2 is a perspectivepartial view of the details in FIG. 1 when soldered together, FIG. 3 isa vertical projection, partly in section, of an apparatus in accordancewith the invention for carrying out the method, combined with a chargingapparatus for the tube element pieces and surface-enlarging members, andwith a driven sawing means for sawing off previously determined groupsof soldered tube element pieces and surface-enlarging members, andfinally FIG. 4 illustrates an alternative embodiment of the apparatusillustrated in FIG. 3, for individually displacing a driving means fordischarging a finished heat exchanger construction after soldering.

Turning now to the FIGS. 1 and 2, a plurality of thin-walled metal tubesare denoted by the numeral 10, preferably brass tubes of a flatconfiguration with a curved contour at the ends. Intermediatesurface-enlarging members are denoted by the numeral 11, and comprisetwo pleated thin metal strips 12 and 13 separated by a thin flat metalstrip 14.

The tube elements 10 are formed with somewhat convex abutment sides 15,intended for being flattened yieldingly under the action of an executedcompression, the peaks of the pleated metal strips being pressed intointimate contact with the whole of the abutment sides 15 of therespective tube element while carrying out a soldering procedure. Auniform soldered joint is thus obtained between the details, so thatuniform heat transmission can take place between them during practicaluse of the heat exchanger, without risk of breaking the soldered joints.

For carrying out the soldering, the tube element pieces 10 can be used,for example, these being covered on the outside with a layer of solder,or solder can be used which has been applied solely to the peaks of thesurface increasing means. The tube element pieces and surface-enlargingmembers joined together in this way are thus intended to form a unitwhere it is especially important that an accurate pitch or uniformspacing is maintained between the centres of the tube elements, sinceduring the construction of the heat exchangers the easy joining of theend portions of the tube elements to other details must be enabled, thelatter being provided with holes for receiving the end portions of thetube elements. The compression during the soldering operation must bevery closely controlled so that good abutment is obtained between thedetails, but also so that no remaining deformation occurs either betweenthe tube element pieces or the surface-enlarging members. Considerationmust be paid in this respect to the alterations in dimensions occurringduring the soldering operation as a result of the increased temperature.

In FIG. 3, which constitutes a schematic partially sectioned verticalprojection of an apparatus for carrying out the method in accordancewith the invention, a schematically illustrated horizontal feed track isdenoted by the numeral 16, on which the tube element pieces 10 and thesurface-enlarging members 11 are advanced. To advance these details inthe direction of the arrow A, there is arranged a belt conveyor 17comprising two endless belts driven in the direction of the arrows B, indriving engagement against the elements 10 and members 11 for advancingthe details intimately abutting each other through a heating zone 18,containing a heating element 19, and also advancing them through acooling zone 20 provided with a fan 21 or other suitable cooling means.During this passage through the heating zone 18 and cooling zone 20 thesolder is first heated to soldering temperature, whereafter the elements10 and the members 11 are cooled to provide formation of a solderedjoint simultaneously as they are kept intimately pressed against eachother. The soldered details are then discharged continuously to theright in FIG. 3, with the help of a discharge apparatus generallydenoted by the numeral 22 comprising endless belts, which are driven inthe direction of the arrows B and advance the soldered details to theright in the Figure. As a final operation, groups of a predeterminednumber of tube element pieces and surface-enlarging members are cut offwith the help of a rotating circular saw 23 driven by a motor 24.

According to the inventive concept, it is important that an active forceis maintained counter to the forced advance of the driving means 17, atthe discharge end drive means 22 to restrain the advance through thecooling zone 20 etc. It is important that a counteracting force ismaintained which is not affected either by the driving movement from thedriving means 17 or from the material movements related to thecoefficients of expansion in the system. A constantly acting counterforce can be provided if the driving means 22, as is shown schematicallyin FIG. 3, is placed on a carriage 25 which is freely movable in the enddirections of the feed track. For this purpose, a pressurizedpiston-cylinder 26 is arranged at the end to the right in FIG. 3, thismeans being stationary and having a piston rod 27 connected to thecarriage 25 at the point 28.

The pressure cylinder 26 has the sole task of maintaining thepredetermined constant force acting on the tube element pieces 10 andthe surface-enlarging members 11, on the feed track 16. The advancingrates for the advancing means 17 and 22 are set individually such thatthe carriage 25 is within the range of action of the pressurizedpiston-cylinder unit 26. The advancing rate can be regulated manually orwith the aid of known control technology.

Several other alternatives are conceivable for providing the constantforce acting on the details placed on the feed track 16.

One example thereof is illustrated in FIG. 4, the same driving means asin FIG. 3 being utilized. Instead of the pressure cylinder 26 and piston27, a freely dependent weight 29 is used, hanging at one end of a cabledenoted by 30, the other end 31 of this cable being attached to thecarriage 25. In this example, the cable runs over a rotatable pulley 33mounted on a stationary shaft 32. With the aid of both these means,advancing through the apparatus can be achieved in a simple way suchthat a constant force always acts in a direction opposing the advancingdirection, and this in turn signifies that a suitable compression of thetreated tube element pieces 10 and surface-enlarging members 11 isobtained in spite of movements due to heat in the treated details andadvancing movements along the feed track 16.

Instead of sawing off the heat exchanger construction discharged as acohesive web, it is naturally within the scope of the invention toarrange, or take such steps that groups of definite numbers of tubeelements and surface-enlarging members are separated by dummies madefrom material preventing soldering during advancing to the heating zone.

The apparatus in accordance with the invention can be alternatelycharged with tube element pieces and surface-enlarging members, inaccordance with methods known per se. One method is to arrange a trough34, as is illustrated to the left in FIG. 3, for automatically advancingelements 10 at predetermined occasions in the direction of the arrow Cto the advancing track, and by means of a chute 35 to feed asurface-enlarging member 11 in the direction of the arrow D atdetermined times, so that the tube element pieces and thesurface-enlarging members are alternately placed in the right order ateach occasion on said track in accordance with the above and areadvanced by the driving means 17 on the feed track.

The invention is not limited to the illustrated and described embodimentexample thereof, but can be varied in different ways within the scope ofthe following patent claims.

I claim:
 1. A method of manufacturing heat exchangers comprising tubeswith substantially rectangular cross-section alternating withintermediate surface-enlarging means in the form of pleated thin metalstrips, which are joined to each other by heating under mutualcompression, the starting material used being tube element pieces andsurface-enlarging means of predetermined length, the tube element piecesand surface-enlarging means mutually engaging with adjacent long sidesin an advancing path, said method comprising: advancing a line of tubesalternating with surface-enlarging means through a heating zone and acooling zone utilizing a first drive means acting in an advancingdirection, uniting said tubes and said surface-enlarging means in saidheating and cooling zones, and discharging united tube element piecesand surface-enlarging means from the cooling zone by means of a seconddrive, which is moved reciprocally as a unit in the path, the seconddrive means exerting a force on the line of tubes and surface-enlargingmeans acting opposite to the advancing direction so as to subject theline to a compressive force during advance of the line through theheating zone and the cooling zone, said metal strips having peaksbrought into intimate contact with said tubes by heating during passagethrough the heating zone and by the compressive force.
 2. A method asclaimed in claim 1, characterised in that the driving movement of thesecond drive means (22) is regulated automatically in relation to thedriving movement of the first drive means (17) in response to theposition the second drive means (22) assumes in the advancing path (16).3. A method as claimed in claim 1 or 2, further comprising insertingspacing means between groups of a predetermined number of tube elementpieces and surface-enlarging means to separate the groups from eachother, the spacing means not being joined to the groups during passagethrough the heating zone and the cooling zone.
 4. A method as claimed inclaim 1 or 2, further comprising mechanically separating groups of apredetermined number of tube element pieces (10) and surface-enlargingmeans (12,13) from the line after the joining operation.
 5. A method ofcontinuous manufacture of heat exchanger members comprising the stepsof:(A) assembling a line having tube elements parallel to each other andalternating with intermediate surface-enlarging means in the form ofpleated thin metal strips; (B) advancing the assembled line through aheating zone and a subsequent cooling zone by means of a drive means;(C) applying a force component to said assembled line acting in adirection counter to the direction of advance of said assembled line,said force component being applied by bringing an engagement means intoengagement with said assembled line downstream of said cooling zone soas to obtain compression of the tube elements and surface-enlargingmeans comprising said assembled line and to keep the assembled linecompressed during a period when the tube elements and surface-enlargingmeans and being joined by soldering in the heating zone and the coolingzone, said engagement means being movable forwardly and rearwardly alongthe path of advance of said assembled line of tube elements andsurface-enlarging means; and (D) applying to said engagement means apredetermined constant force which provides said force component actingon the advancing tube elements and surface-enlarging means.
 6. Method asset forth in claim 5, characterized by operating the engagement means toadvance said line of compressed tube elements and surface-enlargingmeans with a feeding speed slower than the feeding speed of said drivemeans.
 7. Method as set forth in claim 6, characterized by automaticallycontrolling the driving movement of the engagement means in relation tothe driving movement of the driven means in response to the position ofthe engagement means with respect to the advancing path of saidassembled line of joined tube elements and surface-enlarging means.